The present invention relates to a microwave plasma source for forming a film on a target by sputtering such as a semiconductor process technique or a surface treatment.
A conventional microwave plasma source of the sputter-ECR (Electron Cyclotron Resonance) type is disclosed in "Ohyo-butsuri" Vol. 57, published in 1988, on page 1301, by Shigetomi MATSUOKA and Kenichi ONO and is described hereinbelow.
FIG. 3 shows the structural view of the apparatus. In FIG. 3, a resonance chamber 1 is shaped into a cylindrical waveguide operation in a TE112 mode in a vacuum. A microwave field of a frequency of 2.45 GHz is introduced in the resonance chamber 1 from a waveguide 2 through a vacuum sealing window 3. In the resonance chamber 1, a magnetic field intensity of 875G is applied to the microwave field of 2.45 GHz by an outer coil 4 in order to satisfy a specified ECR condition. Then, an electrical discharge gas, such as argon, is introduced in the resonance chamber 1 through a gas inlet 5. A cylindrical target 8 is arranged under the resonance chamber 1 while contacting a plasma extraction hole 6 of the resonance chamber 1 so as to surround a plasma flow 7. A substrate holder 9 and a substrate held on the substrate holder 9 are arranged under the target 8.
The operation of the apparatus is described hereinbelow.
Argon is used as an electrical discharge gas and a plasma is produced in the resonance chamber 1 within the pressure range of 10.sup.-4 -10.sup.-3 Torr. The plasma flows out as the plasma wave 7 of several electron volts to tens of electron volts, i.e., the plasma wave 7 with lower energy ions flows through the plasma extraction hole 6 in accordance with divergence magnetic field gradient of the coil 4. At that time, a negative DC voltage or RF energy (at a frequency of 13.56 MHz) is applied to the target 8, and then, ions in the plasma flow 7 are injected on the surface of the target 8 to generate sputtering. Some of the particles sputtered from the target 8 flow towards the target 10 to form a thin film thereof.
However, the above-described apparatus has the following disadvantages. The apparatus is large in size because a coil is used for generating the magnetic field and the plasma generating section and the sputtering section are separated from each other. Furthermore, it is difficult to produce a ring-shaped target.